Dear Thinfor,
There were two birds chasing each other deep inside the trees. Both were 'dancing' with high frequency by moving their wings ups and downs (and you could see them in the photos). They sounded like a Rufous-capped babbler but with a quickened tempo and non-stop for a long period (about 20 to 30 seconds)while dancing. Then they flew away and I found them (two of them) again later in nearby trees. Later, one of them stood out openly (seemingly resting) for around 30 seconds and I took a few photos.
I may not be very familar with the sound of Rufous-capped babbler from the beginning (I only heard it two times in TPK). After all, I might just mis-associate the sounds. In any csse, thank you very much for your guidance.
Attached with two more photos for sharing. Case closed. I learnt a lot. Thank you.